With turbomachines, and especially turbines with untwisted blades, the degree of reaction of the stages across the spread of the blade locally deviates from the average design degree of reaction. The degree of reaction reduces towards the hub in relation to the center section, while it increases towards the casing. In this case, a decreasing degree of reaction signifies a relative increase of the pressure drop across the stator blade row of the stage, while an increased degree of reaction signifies a relative increase of the pressure drop across the rotor blade row. That is to say the pressure difference across a blade ring becomes large in each case at the blade tips at which the leakage losses are large anyway as a result of overflow, and sensitively react to pressure differences.
The increased leakages over the blade tips of the stator blades at the hub on the one hand, and over the blade tips of the rotor blades at the casing on the other hand, can be countered by the blade airfoils being tilted by an angle of inclination from the purely radial orientation. The overflow losses for example can be reduced by the blade airfoils of the stator blades being inclined by several degrees towards the hub by their pressure face. By the same token, the overflow losses are also reduced if the blade airfoils of the rotor blades are inclined by several degrees towards the hub by their suction face. By means of the inclination of the blade airfoils, additional radially oriented pressure fields are induced in the blade passages. Consequently, however, for example with stator blade passages in the region of the casing, it results in a secondary flow field being drawn further into the core flow, which leads to an increase of the secondary flow losses.
By means of inclining the blade airfoils, therefore, the overflow losses are reduced, but on the other hand the secondary flow losses increase so that their increase soon quickly overcompensates the reduction of the overflow losses. By means of an inclination of the blade airfoils, therefore, comparatively tight practical limits are set upon the reduction of the overflow losses.